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Abstract — Today’s IP backbones are provisioned to provide excellent performance in terms of loss, delay and availability. However, performance degradation and service disruption are likely in the case of failure, such as fiber cuts, router crashes, etc. In this paper, we investigate the occurence of failures in Sprint’s IP backbone and their potential impact on emerging services such as Voice-over-IP (VoIP). We first examine the frequency and duration of failure events derived from IS-IS routing updates collected from three different points in the Sprint IP backbone. We observe that link failures occur as part of everyday operation, and the majority of them are short-lived (less than 10 minutes). We also discuss various statistics such as the distribution of inter-failure time, distribution of link failure durations, etc. which are essential for constructing a realistic link failure model. Next, we present an analysis of routing and service reconvergence time during a controlled link failure scenario in our backbone. Our results indicate that disruption to packet forwarding after link failures depends not only on routing protocol dynamics, but also on the design of routers ’ architectures and control planes. Thus our results offer insights into two basic components for defining network-wide availability, which we consider a more appropriate metric for service-level agreements to support emerging applications. I.

Citations

...paper, we attempt to address this deficiency by analyzing link failures in Sprint’s operational IP backbone. Our contribution is two-fold. In the first part of our work we study IS-IS routing updates =-=[4]-=- collected using a passive IS-IS “listener” over a four-month period. We analyze the frequency and duration of link failures as re-ported in IS-IS Link State PDUs (LSPs). We also report various stati...

... and the instant when new routing tables are available to the router. Service disruption time refers to the duration between the time at which packet forwarding stops and the time when it resumes. In =-=[1]-=-, the authors have identified three components that contribute to IS-IS convergence delay: failure detection, LSP propagation and SPF computation. However, we found that there are additional steps inv...

...e U.S. West Coast, across the backbone network. The shortest path taken by these probes traverses three different POPs. The probes are 200 byte long UDP packets and are sent every 5 ms. Two DAG cards =-=[3]-=- capture and timestamp the packets on their way to the end systems. During a maintenance window (around midnight), we shut down two backbone links connecting two POPs along the path of the packet prob...

... due to the loss of a sequence of IS-IS Hello packets. 2. Initial delay before the IS-IS stack is notified of the link status change. In Cisco routers this is defined by the carrier-delay timer value =-=[2]-=-. This timer is used to filter out very short and transient link flaps. 3. Initial wait to generate a new LSP that informs other routers about the event. This is determined by another timer: lsp-gen i...